The embodiments described herein relate generally to power equipment protection devices and, more particularly, to apparatus for use in channeling exhaust gases and pressure away from a location of arc generation.
Known electric power circuits and switchgear generally have conductors that are separated by insulation, such as air, or gas or solid dielectrics. However, if the conductors are positioned too closely together, or if a voltage between the conductors exceeds the insulative properties of the insulation between the conductors, an arc can occur. The insulation between the conductors can become ionized, which makes the insulation conductive and enables formation of an arc flash.
An arc flash includes a rapid release of energy due to a fault between two phase conductors, between a phase conductor and a neutral conductor, or between a phase conductor and a ground point. Arc flash temperatures can reach or exceed 20,000° C., which can vaporize the conductors and adjacent equipment. Moreover, an arc flash can release significant energy in the form of heat, intense light, pressure waves, and/or sound waves, sufficient to damage the conductors and adjacent equipment. However, the current level of a fault that generates an arc flash is generally less than the current level of a short circuit, such that a circuit breaker may not trip or exhibits a delayed trip unless the circuit breaker is specifically designed to handle an arc fault condition.
Standard circuit protection devices, such as fuses and circuit breakers, generally do not react quickly enough to mitigate an arc flash. One known circuit protection device that exhibits a sufficiently rapid response is an electrical “crowbar,” which utilizes a mechanical and/or electro-mechanical process by intentionally creating an electrical “short circuit” to divert the electrical energy away from the arc flash point. Such an intentional short circuit fault is then cleared by tripping a fuse or a circuit breaker. However, the intentional short circuit fault created using a crowbar may allow significant levels of current to flow through adjacent electrical equipment, thereby still enabling damage to the equipment.
Another known circuit protection device that exhibits a sufficiently rapid response is an arc containment device, which creates a contained secondary arc to divert the electrical energy away from the arc flash point. For example, some known devices generate an arc, such as a secondary arc flash within an arc containment device or vessel, for use in dissipating energy associated with a primary arc flash detected on a circuit. At least some known arc containment devices include a metallic top or cover to withstand the high pressure, and extremely high temperature gases generated at the location where the arc is created. However, such containment devices can be damaged, or exhibit arc tracking to ground, due to the high temperature conductive gases and conductive residue generated within the device. During the secondary arc flash, hot ionized exhaust gases at high pressure are created. The exhaust gases exert significant thermal and mechanical stress on the cover. The high pressures generated within the arc containment device necessitate a strong robust material be used to form cover. However, while rigid covers, such as those formed from metal such as steel or aluminum, provide the necessary structural strength to withstand the high pressure in the arc containment device, the high temperature exhaust gases can cause damage to the metal, such as melting or burn-through. Other metals with higher melting temperatures, such for example as stainless steels, add increased costs and weight, and are therefore not desirable as cover materials. It is desirable to provide a coating that thermally insulates the cover from the high temperatures. Additionally, the ionized exhaust gases deposit soot or other conductive residue on cover that reduce resistance to arc tracking that may lead to a failure due to short circuit to ground, such as to a grounded frame. It is desirable to provide an arc containment device that is robust enough to withstand high pressure, resistant to high temperature, and of sufficiently high resistance to electrical tracking to isolate the top cover from ionized gases to protect against arc tracking failure, for example, to ground.
One known way to provide thermal protection to a metallic substrate is to apply a plasma spray thermal barrier coating to the metal. However, the compositions of conventional thermal barrier coatings as disclosed in the prior art have not additionally addressed the need for the desired increased arc tracking resistance to avoid ground strikes and low cost needed for the arc containment device
For at least the reasons stated above, a need exists for an arc containment device having an improved resistance to melting. Additionally, for at least the reasons stated above, a need exists for an arc containment device having an improved resistance to arc tracking. It would further be desirable for an improved device that is simple, robust, inexpensive, and without moving parts.